The union spokesperson added: "This is a reasonable request and our members are frustrated at the intransigence of management.

"We now hope that management will act to resolve this issue quickly."

The role of visitor experience assistant is an active one in which staff move around the museum to welcome and engage with our visitorsJulie Matthews, head of visitor experience

Labour MSP Neil Findlay has accused the management of "confrontational" behaviour towards the union and warned the reputation of one of Scotland's most popular museums could be damaged by the treatment of its workers.

The Lothian MSP echoed the PCS's call and added: "The National Museum of Scotland is one of our key cultural attractions in Scotland.

"In recent years the management have taken a confrontational line in their dealings with trades unions there representing employees, first over weekend allowances and now over working conditions.

"The management really need to think again about the way they are conducting industrial relations otherwise the reputation of the museum will suffer."

Julie Matthews, head of visitor experience at National Museums Scotland, said management had a constructive relationship with the union.

She said: "The role of visitor experience assistant is an active one in which staff move around the museum to welcome and engage with our visitors.

"However, staff have access to seating throughout the galleries and anyone with additional needs is supported on an individual basis."